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Note that the Ring Indicator is used by the A3LA-RM to indicate that a Mobile Terminated SBD (MT-SBD)
message is queued at the gateway. Application developers can monitor this pin and apply appropriate AT
commands to the A3LA-RM to retrieve the MT-SBD message.
3.2 RS232 Data Interface (3-Wire Configuration)
A 3-wire RS232 data interface may also be implemented. Because of risk of over-run and data loss
especially at high baud rates, the 9-wire interface is the recommended implementation. Several steps must
be taken to allow 3-wire configuration (i.e. only using S_TX, S_RX, and SIGNAL GND). These steps ensure
the A3LA-RM and DTE to work together without having hardware handshaking.
1.
The modem’s DTR line must be held high. Using the modem’s input voltage is fine for this purpose
BUT ONLY if the input voltage is less than 5VDC (see important note below). Looping back the
modem’s DSR line to DTR line will NOT work. The DSR line on the modem should be left
unconnected.
2.
Disconnect the CTS, DCD, DSR, DTR, RTS and RI lines between the DTE and modem.
3.
AT&Dn must be set to AT&D0 to ignore the DTR input from the DTE.
4.
AT&Kn must be set to AT&K0 for no flow control.
5.
The setting can be stored on the modem permanently (until another setting overwrites it) so that it
remains after a power cycle. The modem allows two profiles in which settings are stored, and user
can choose either as a default profile. The relevant commands are &Wn and &Yn. &Wn stores the
present configuration in profile <n>, where <n> can be either 0 or 1. &Yn designates which profile
is loaded after reset or power-up, again <n> is either 0 or 1.
6.
Any needs of the DTE must be addressed separately.
WARNING:
DO NOT use the modem’s input voltage to bring the DTR line high when the
input voltage is higher than 5VDC. Supplying voltage higher than 5VDC to the DTR line will
permanently damage the A3LA-RM.
NOTE:
The Iridium’s Direct Internet service when using the Windows-based Apollo client
requires DCD to be present; hence it is incompatible with a 3-wire serial configuration. The
Direct Internet with Apollo client is available only on the EMSS DoD gateway and NOT on
the commercial gateway.
3.3 DC Power Input
The DC power input is through pin 4 & 16 (EXT_B+) and pins 3 & 17 (EXT_GND). Note that two pins are
provided for the external DC input and two pins are also provided for the associated external ground input.
This is done to distribute the current across two wires, and therefore all four pins should be utilized in the
external power connection. Cables used to supply power to the A3LA-RM should be kept as short as possible
to prevent significant voltage drop, which can cause the A3LA-RM to malfunction during a data call, an SMS
session or an SBD session. Power reset by the A3LA-RM during a call is an indicative of the DC power source
unable to sustain voltage above 4.0V at peak current demand. Appendix E provides the electrical power
profile of the A3LA-RM.